An X-ray source is a device that produces X-ray. It is composed generally of an X-ray tube, a power supply and control system, cooling and shielding and other accessories, with the X-ray tube being the core. The X-ray tube is usually composed of a cathode, an anode, a glass or ceramic housing. The cathode is a directly heated spiral tungsten filament which, when in operation, has current passes through and is heated up to the working temperature of about 2000K, thereby generating a thermally emitted electron beam stream. The cathode is surrounded by a metal cap that opens a slot in the front and enables electron focusing. The anode is a tungsten target inlaid at the end surface of a copper billet, and when in operation, a high voltage of hundreds of thousands of volts is applied between the anode and the cathode. The electrons generated by the cathode accelerate and fly to the anode under the action of the electric field, and hit the target surface, thereby producing X-ray.
X-ray is widely applied in such fields as industrial nondestructive examination, security check, medical diagnosis and treatment. In particular, the X-ray imaging device that makes use of the strong penetrating power of X-ray plays a vital role in every aspect of our daily life. At the early stage, said device was a planer X-ray imaging device of film, but now is the advanced digital 3D imaging device of high definition and multi-angle of view, e.g., computed tomography (CT), capable of acquiring 3D graphics or section images of high definition, being an advanced high-end application.
In a CT device (such as industrial defect detection CT, baggage inspection CT, medical diagnosis CT and so on), it is usual to put the X-ray source at one side of the object under inspection and a detector for receiving ray at the other side. When X-ray passes through an object, its strength varies with such information as the thickness and density of the object. The strength of X-ay received by the detector includes the structural information of one angle of view of the object under inspection. If the X-ray source and detector rotate around the object under inspection, we can acquire the structural information of different angle of view. Restructuring said information by a computer system and software algorithm can obtain a 3D image of the object under inspection. At present, the CT device is securing the X-ray source and detector to a circular slip ring surrounding the object under inspection. Every round of movement in work can get an image of a section of one thickness of the object under inspection, which is called a section. The object under inspection then moves along the direction of thickness to obtain a series of sections, which put together is just a fine 3D structure of the object under inspection. Therefore, for an existing CT device, in order to acquire information of different angle of view, it has to change the position of the X-ray source, so the X-ray source and detector need to move on the slip ring. To step up the inspection, the moving speed of the X-ray source and detector is often very fast. Due to the high speed movement on the slip ring, the overall reliability and stability of the device are reduced. Besides, as hindered by the moving speed, the CT inspection speed is also limited. Although the newest generation of CT in recent years mounts the detector in a circumferential manner such that the detector does not have to move, the X-ray source still has to move on the slip ring. Besides, multiple rows of detectors may be mounted so that a plurality of section images can be obtained every round the X-ray source moves, thereby increasing the CT inspection speed, but this does not solve the problem resulted from the movement on the slip ring fundamentally. Therefore, the CT device is need of an X-ray source capable of producing multiple angles of view without having to shift position.
Besides, in order to improve the inspection speed, it is usual that the electron beam produced by the cathode of the X-ray source has long and continuous high power bombardment on the anode tungsten target. However, because the target spot has a small area, the heat radiation of the target spot also becomes a big problem.
To solve the reliability and stability problem as well as the inspection speed problem and the anode target sport heat radiation problem brought about by the slip ring of the current CT device, existing patent documents propose some methods, such as rotary target X-ray source, which can solve the problem of overheating of the anode target to a certain extent, but its structure is complex and the target spot producing X-ray is still a definitive target spot position relative to the whole X-ray source. For example, in order to achieve multiple angles of view for a fixed X-ray source, some techniques arrange a plurality of independent traditional X-ray sources in a compact way on a circumference to displace the movement of the X-ray source. This may achieve multiple angles of view, but is too costly, and because the space between target spots of different angles of view is large, the image quality (3D resolution) is quite poor. In addition, the patent document 1 (U.S. Pat. No. 4,926,452) brings forward a light source and method for producing distributed X-ray, wherein the anode target has a very large area that alleviates the problem of the target overheating, and the target spot positions changing along the circumference can produce many angles of view. Although the patent document 1 is to scan and deflect the accelerated high energy electron beam, having the problem of being difficult to control, the locations of the target spots being not discrete and poorly repeatable, it is still an effective method capable of producing distributed light source. Moreover, the patent document 2 (US20110075802) and the patent document 3 (WO2011/119629) bring forward a light source and method for producing distributed X-ray, wherein the anode target has a very large area that alleviates the problem of the target overheating, and the target spots are scattered and fixed and arranged in an array, being able to produce many angles of view. Besides, carbon nano-tubes are used as the cold cathodes, the cold cathodes are arranged in an array, using the voltage between cathode grids to control field emission, thereby controlling every cathode to emit electrons in order, and bombard the target spots in a corresponding order of positions on the anode, thus becoming a distributed X-ray source. However, there are still such shortcomings as complex production process and insufficient capacity of emission and service life of carbon nano-tubes.